- Chemical change
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Chemical changes occur when objects or substances are changed or altered. In a chemical change, particles of the original materials collide with one another. Some exothermic reactions may be hot enough to cause certain chemicals to also undergo a change in state. For example, in the case of aqueous solutions, bubbles may not necessarily be newly produced gas but instead water vapor, so, chemical change is nothing but a change which is usually irreversible.
When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated. An example of a chemical change is the reaction between sodium hydroxide and hydrogen chloride to produce sodium chloride, or common salt. This reaction is so exothermic, meaning it releases heat in the form of energy, that even flames are generated. This is an example of a chemical change because the end product is molecularly different from the starting molecules.
Chemical changes are happening all the time. There are several different types of chemical change, including: synthesis, decomposition, single displacement, double displacement, neutralization, precipitation, combustion and redox.
Examples of chemical changes:
- Neutralization (Mixing an acid with a base, resulting in water and salt).
- Photosynthesis – a process in which carbon dioxide and water are changed into sugars by plants.
- Cracking heavy hydrocarbons to create lighter hydrocarbons (part of the process of refining oil).
- Cooking examples: cake, pancakes, and eggs/bacon
- Oxidation examples: rust or tarnishing
- Ripening examples: bananas, tomatoes or potatoes
Evidence of a chemical change:
The following can indicate that a chemical change took place, although this evidence is not conclusive:
- Change of odor.
- Change of color (for example, silver to reddish-brown when iron rusts).
- Change in temperature or energy, such as the production (exothermic) or loss (endothermic) of heat.
- Change of form (for example, burning paper).
- Light, heat, or sound is given off.
- Formation of gases, often appearing as bubbles.
- Formation of precipitate (insoluble particles).
- The decomposition of organic matter (for example, rotting food).
A chemical change is a change in which one or more substances are converted into different substances.
A chemical change can have a huge impact on a physical change. Chemical changes are permanent.
A chemical change changes the identity or properties of a substance and cannot easily be reversed.
Chemical bonds Intramolecular
("strong")Cation–pi bond · Salt bond
("weak")Other noncovalentNote: the weakest strong bonds are not necessarily stronger than the strongest weak bonds
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